Convection vs Conduction in Dry Herb Vaporisers

Most patients prescribed cannabis flower in Australia are told to vaporise it rather than smoke it, and are then left to work out the device on their own. The single most useful thing to understand about a dry herb vaporiser is how it moves heat into the plant material, because that one design decision drives almost everything else: how you pack the chamber, how fast you draw, whether you need to stir, and how much of your prescription you actually get to use.

There are two ways of doing it, and a third that mixes them. This article is general information about how the devices work and is not a substitute for individual medical advice.

Key takeaways

• Conduction heats by contact. The chamber wall gets hot and the flower touching it heats first.
• Convection heats by moving air. An element warms incoming air and that air carries the heat through the material as you inhale.
• Conduction is faster to start and simpler; convection is more even and generally tastes cleaner.
• The two want opposite packing. Conduction wants a firm, well-contacted pack; convection wants a looser one so air can move through it.
• Most current devices are hybrids, and the honest way to tell what you own is the evenness of the material after a session.
• Neither type is a health claim. Vaporising avoids combustion, but it is not risk free and any respiratory symptom belongs in a conversation with your doctor.

Conduction: heat by contact

In a conduction vaporiser, the chamber itself is the heater. A ceramic or metal oven is brought up to temperature, your flower sits against it, and heat moves from the hot surface into the plant material by direct contact, the same way a pan heats food.

What it does well. It heats up quickly, often in well under a minute. It is mechanically simple, which makes it cheaper and means fewer things to go wrong. It works well as a session device, where you load once and take several draws over a few minutes. And because the heat is already in the material, the draw does not have to work hard: you get vapour whether you inhale slowly or quickly.

Where it struggles. Contact heating is uneven by nature. The material pressed against the wall is hottest, the material in the middle of the chamber is coolest, and if the temperature is set high the outer layer can scorch or even combust while the centre is barely warm. Conduction chambers also keep cooking between draws, because the oven stays hot and the flower is still touching it. Leave a loaded conduction device sitting at temperature and you are using up your material with nothing to show for it.

How to use one well. Pack firmly and evenly so every part of the load touches something hot, without crushing it into a plug that airflow cannot pass. Stir between draws, or knock the chamber to redistribute the load. Keep sessions continuous rather than letting a hot chamber idle. And run cooler than you think you need to, because the material at the wall is hotter than the number on the screen.

Convection: heat by moving air

In a convection vaporiser, the flower does not touch the heating element at all. An element heats incoming air, and that hot air is pulled or pushed through the chamber, giving up its heat to the plant material as it passes.

What it does well. Every surface of every piece of material meets air at roughly the same temperature, so extraction is far more even and the material tends to finish uniformly rather than in a gradient. Flavour is usually better, especially early in a session when the lighter terpenes come off, which matters if you care about the terpene profile of a product. It is also closer to on demand: no air moving means little heat reaching the flower, so a chamber left sitting is not quietly cooking itself.

Where it struggles. Moving enough hot air takes power. Convection devices tend to be pricier, and portable ones either carry a bigger battery, run a fan, or need a longer heat up. Your draw technique matters much more, because you are the pump. Draw too fast and the air does not spend long enough at the element, so it arrives cooler than the display suggests and you get thin vapour at what looks like a high setting.

How to use one well. Pack loosely enough that air can move through the whole load, but not so loosely that the material rattles around in a mostly empty chamber. Draw slowly and steadily. If the vapour is thin at a temperature that should be producing plenty, the usual cause is drawing too fast or packing too tightly, not a faulty device.

Hybrids, and why almost everything is one

Very few devices are purely one thing. A convection device with a chamber that sits next to a hot element is getting some conduction whether the marketing mentions it or not. Plenty of conduction devices route the incoming air past a heater on its way in, adding a convective component.

Hybrids exist because the two approaches fail in complementary ways. Conduction gives you a fast start and a forgiving draw; convection gives you evenness and flavour. A hybrid aims for a quick heat up with less of the scorching and less of the between-draw waste.

The practical takeaway is not to trust the label. The material tells you the truth.

Reading your spent flower

When a session is done, tip the chamber out onto something pale and look at it.

Even, uniform light to mid brown across the whole load means the heat reached everything at about the same rate. That is what you want, and it points to convection or a well behaved hybrid.

A gradient, darker at the edges and greener in the middle, is contact heating that has not been stirred. Nothing is wrong with the device; the load simply was not redistributed.

Black, brittle or ashy material, or any smell of smoke, means part of the load combusted. That is the outcome vaporising is meant to avoid. Lower the temperature, pack a little less densely, and stir more often.

Still green after a full session means the heat never really arrived. On a convection device that usually means drawing too fast or packing too tight. On a conduction device it usually means the load was too loose to make good contact, or too deep for the chamber.

What this changes about temperature

Whichever type you have, the number on the display is the temperature of the oven or the element, not the temperature of your flower. In conduction the material at the wall runs hotter than the setting and the centre runs cooler. In convection the air loses heat on its way through the load, so the material sees less than the element produced, and it sees less again the faster you inhale.

This is why the same setting on two devices behaves so differently, and why comparing temperatures with another patient is close to meaningless unless you both have the same device. Find the range that works on your own equipment and record it.

The general principle still holds: lower temperatures release the lighter, more volatile terpenes and give a milder effect, while higher temperatures extract more cannabinoid but at the cost of flavour and with more irritation. Working upwards through a session rather than starting at the top gets you both ends of that range from a single load. There is more on preparation and grind in the guide to checking flower quality and preparing it for your vaporiser, and on device basics in the guide to using a dry herb vaporiser.

Maintenance is not optional on either type

Both designs lose performance as residue builds up, but they lose it differently.

Conduction chambers accumulate a resin layer on the oven wall, and that layer sits between the heater and your flower. As it thickens, less heat gets through, and patients often respond by turning the temperature up, which bakes the residue harder. Cleaning the chamber restores the original behaviour and usually means you can turn the setting back down.

Convection devices are more sensitive to blocked airflow. Screens, filters and vapour paths clog, and because convection depends entirely on air moving through the load, a partly blocked screen shows up immediately as weak vapour and a hard draw. If a convection device suddenly feels underpowered, check the screen before anything else.

The honest limits

Choosing a heating style is a comfort and efficiency decision, not a clinical one. Vaporising avoids the combustion products that come with smoking, and that difference is measurable rather than theoretical: a small clinical study comparing the two routes found carbon monoxide exposure, measured as carboxyhaemoglobin in the blood, was dramatically lower after vaporising than after smoking the same material. That is the reason vaporising is the usual route for prescribed flower in Australia.

It is still not risk free, and it is not a treatment in itself. Avoiding combustion removes one category of harm; it does not make an inhaled product harmless, and the long term respiratory picture for vaporised cannabis is not well characterised. Inhaled medicine can irritate the airways regardless of how the heat was delivered.

If you cough persistently, get chest tightness, or find your breathing has changed since starting an inhaled product, that belongs in an appointment rather than in a device upgrade. The route of administration is part of the prescribing decision, and if inhalation is not suiting you there are other formulations to discuss with your doctor.

Frequently asked questions

Is convection better than conduction for a dry herb vaporiser?

Convection generally gives more even extraction and cleaner flavour, and it wastes less material between draws. Conduction heats faster, costs less and is more forgiving of how you inhale. Neither is better in every respect, and most current devices combine the two. The right choice depends on whether you value flavour and efficiency or speed and simplicity.

How can I tell whether my vaporiser is convection or conduction?

Look at the spent material after a session. Convection tends to finish evenly, in a uniform light to mid brown. Conduction leaves a gradient, darker where the flower touched the chamber wall and greener in the middle, unless you stirred. A device that keeps producing vapour with no air moving through it is heating by contact.

Does a conduction vaporiser burn cannabis?

It should not, but it can if the temperature is set too high or the chamber is packed against the wall. The material in direct contact with the heater runs hotter than the display setting, so the outer layer can scorch before the centre is properly warm. Black or ashy material and any smell of smoke mean part of the load combusted.

Why is my convection vaporiser producing thin vapour?

The two usual causes are drawing too fast and packing too tightly. Convection depends on air passing over the element and then through the load, so a quick draw gives the air less time to pick up heat, and a dense pack stops it moving through at all. A clogged screen or filter produces the same symptom, so check that before assuming a fault.

Which type of vaporiser preserves terpenes better?

Convection, generally, because the load heats evenly rather than from the outside in and there is less scorching of the material against a hot surface. Terpenes are volatile, and the lightest ones come off at the lower end of the range, so a device that lets you start low and work upwards will show them off best whichever way it heats.

Should I ask my doctor which vaporiser to use?

Your doctor advises on the medicine and the route of administration rather than on specific hardware. It is still worth raising, because how you are taking a prescribed product affects how it works and whether it suits you. If inhalation is causing problems, that is a clinical conversation, and it is one to have at a scheduled follow-up appointment rather than left until the next repeat.